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Otolith atlas of fish of the Sinos River/Atlas de otolitos de peixes do Rio dos Sinos.

1. Introduction

Otoliths are paired structures composed of organic matter and calcium carbonate crystals, especially in the form of aragonite. These structures are located in the membranous labyrinth in the inner ear of fishes and are responsible for sound detection and maintenance of balance (Lecomte-Finiger, 1999; Garcia et al., 2004; Payan et al., 2004; Popper et al., 2005).

The inner ear consists of three pairs of chambers, each containing an otolith. The otolith called lapilli occupies the utricular vestibule, the sagittae occupies the saccular and the asterisci the lagenar vestibule (Secor et al., 1991; Gomiero and Braga, 2007). Each pair is different in shape and appearance, and in most adult fish the sagittae are larger and have the largest morpholigical variability (Campana, 2004; Tuset et al., 2008).

Otoliths are formed from a primordial secreted by the inner ear, and are usually the first calcified structure formed during ontogenesis (Morales-Nin, 2000; Wright et al., 2002). The formation involves rhythmic variations in the deposition and size of the organic matrix fibre, which results in the formation of concentric layers of variable thickness (Morales-Nin, 2000). These layers alternate in opaque and hyaline layers, representing periods of fast growth and slow growth, respectively; in temperate zones a pair of these layers consists of a year, and this set of layers is called annulus, and it is used for the age determination in years (Wright et al., 2002).

The characteristics, shape and growth pattern of otoliths are highly species specific and very similar between individuals (Frost, 1981; Hunt, 1992; Anguirre and Lombarte, 1999). Their chemical composition and microstructure are directly related to environmental conditions, so in addition to the identification of different species it is possible to differentiate between stocks (Lecomte-Finiger, 1999).

Furthermore, otoliths can resist the passage through the digestive tract of ichthyophagous species because of their low degradability. Thus they have been used as an important tool for studies of stomach contents (Frost, 1981; Gomiero and Braga, 2007).

In Brazil there are only otolith catalogs of marine fish, such the work of Correa and Vianna that in 1992/93 described the otoliths of the family Scianidae from the coast of Parana. The same study lists only five previous studies of isolated morphological descriptions. In 1995 Lemos et al. (1995a, b), published two catalogs, which describe the otoliths of the family Engraulidade and Cupleidae, both of the coast of Parana.

The purpose of this work is to provide a photographic guide of the sagittae otoliths of the most common fish species from the Sinos river. The intention is to provide a visual reference which may serve as basis for studies of stomach contents of ichthyophagous species.

2. Materials and Methods

The fish used in this investigation were sampled in different projects of the Laboratory of Fish Ecology UNISINOS. All the fish were captured in the Sinos River by electrofishing or gill nets (meshes 15 mm to 60 mm) between the years of 2006 and 2007. All individuals were measured (standard length, SL), weighed and stored on ice until the removal of otoliths. Only the pair of sagittae was removed.

After removal, the otoliths were washed in water and stored in glass tubes that had remained open for about 15 days to ensure that the otoliths completely dried.

Otoliths were measured (otolith length - OL) and photographed in pairs in a way that both sides were visible. The photographs were taken with a Leica Stereo Macroscope attached to a video camera, connected to a computer with the image analysis program Leica Application Suite v3.7.

3. Results

In this work we photographed the otoliths of 36 species from 15 families distributed in five orders. Four of these species do not belong to the native fish community of the Sinos river basin. Two are exotic (Micropterus salmoides and Orechromis niloticus), one is invasive (Pachyurus bonariensis) and another one allochthonous (Piaractus mesopotamicus) (Leal et al., 2009).


Anostomidae (Figure 1 and 2)

Characidae (Figure 3-10)

Curimatidae (Figure 11)

Erythrinidae (Figure 12)

Prochilodontidae (Figure 13)


Engraulididae (Figure 14)


Gymnotidae (Figure 15)


Centrarchidae (Figure 16)

Cichlidae (Figure 17-24)

Sciaenidae (Figure 25)


Callichthyidae (Figure 26-28)

Heptapteridae (Figure 29 and 30)

Loricariidae (Figure 31-33)

Pimelodidae (Figure 34 and 35)


Synbranchidae (Figure 36)

4. Discussion

As reported by Torno (1976) species of the same genus may have very similar otoliths. In this study it was shown that Gymnogeophagus gymnogenys and G. labiatus and also Crenicichla lepidota and C. puntacta have otoliths that are almost not differentiable.

When considering families, it was possible to identify common features in their morphology. In the families Cichlidae and Characidae, for example, the shape of otolith is very similar in all species. Correa and Vianna (1992/93) reported the existence of such common features within families, characteristics like common shape, location of the sulcus, form of the ostium and otolith tail.

When using otoliths for species identification it should be remembered that the shape and size of the otolith may differ in different life stages of individuals. Most larval stages do not display a specific shape. The final shape is defined only in the juvenile stage (Campana, 2004).

The similarity of otolith shape may impede the exact identification of species in some cases (Tuset et al., 2008). However, with this atlas it may be possible to have a handy visual reference for an easy identification of the diet of ichthyophagous species of the Sinos river and also adjacent basins with similar fish assemblies.

Received June 29, 2012 - Accepted February 26, 2013 - Distributed May 31, 2014 (With 36 figures)


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Bremm, CQ. and Schulz, UH. *

Laboratorio de Ecologia de Peixes, Universidade do Vale do Rio dos Sinos - UNISINOS, Avenida Unisinos, 950, CEP 93022-000, Sao Leopoldo, RS, Brazil

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Title Annotation:Original Article
Author:Bremm, C.Q.; Schulz, U.H.
Publication:Brazilian Journal of Biology
Date:May 1, 2014
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